The present invention is concerned with the catalytic inducement of the reaction of the oxirane groups of a polyepoxide with carboxylic acids. Generically the invention is directed to the preparation of a terminally unsaturated polyester from a polyepoxide, a dicarboxylic acid and an unsaturated monocarboxylic acid. Such polyesters, which are known, as, for example, in U.S. Pat. No. 2,256,226 have a spectrum of properties making them valuable in a wide variety of end uses. When a small amount of relatively long chain saturated monocarboxylic acid is used to replace a part of the unsaturated acid, the products are especially well adapted for use in radiation curable printing inks and coatings as shown in the copending application of Bogan and Hickner, U.S. Ser. No. 644,693 filed Dec. 29, 1975.
The general reaction of an oxirane and a carboxyl group has been known for a long time as exemplified by U.S. Pat. No. 2,929,835 wherein the reaction was catalyzed by inorganic bases and by amino compounds. More specifically, the reaction of an ethylenically unsaturated monocarboxylic acid with a diepoxide was taught in U.S. Pat. No. 3,066,112 wherein tertiary amines, such as dimethyl-para-toluidine; and para-toluene sulfinic acid were used as catalysts.
The use of compounds containing an ionizable atom of iron or chromium as a catalyst for the reaction was taught in British Pat. No. 871,767.
Trivalent chromium salts or amines as catalysts for preparing flexible vinyl ester resins is noted in U.S. Pat. No. 3,933,935.
Phosphonium, sulfonium or ammonium salts of inorganic acids are employed as catalysts for the reaction in U.S. Pat. No. 3,377,406.
All of the prior art catalyst systems suffer from one or more disadvantages when applied to the tricomponent monomer mix of this invention.